From CBS News:

The Kerry campaign was slow in countering the Swift Boat charges, the allegations persisted and Kerry’s bad August ensued.

Kerry led most polls leading into August. By the second week of September, President Bush had come back and now has a four-to-seven point lead over Kerry, depending on the poll.

I’m just not sure that I buy this argument. I’m sure the Swift Vets are hurting Kerry, but deeper down I think the real reason he’s slipping is that as August progressed and people came home from their summer vacations and got back to work, they started really looking at Kerry and don’t like what they see.